Gold alloys



Patented May 13, 1952 GOLD ALLOYS Joseph M. Williams, Attleboro Falls,Mass, assignor to Metals & Controls Corporation, Attleboro, Mass, acorporation of Massachusetts No Drawing.

Application September 10, 1949,

Serial No. 115,111

6 Claims. 1

This invention relates to gold alloys.

Among the several objects of the invention may be noted the provision ofa gold alloy which may be used to manufacture either solid gold objectsor gold-plated objects, which gold alloy has a greater resistance tostress-corrosion than other gold alloys of similar color and karat; theprovision of a gold alloy of the class described which is harder, workhardens less, and wears better when subjected to the wear normallyencountered by articles of jewelry, than other gold alloys of similarkarat and color; and the provision of a gold alloy which, while havingthe characteristics outlined above, is simple to make and whosemanufacture lends itself to already existing techniques of gold alloymaking. Other objects will be in part obvious and in part pointed outhereinafter.

The invention accordingly comprises the ingredients and combinations ofingredients, the proportions thereof, and features of composition, whichwill be exemplified in the products hereinafter described, and the scopeof the application of which will be indicated in the following claims.

One of the serious problems existing in regard to gold alloys for thejewelry industry, is that of stress-corrosion. By stress-corrosion ismeant, without going into great detail, the phenomenon that when thesurface of a metal is under tensile stresses, cracking of the metal bycorrosive elements in contact with it is enhanced and greatly speeded.During the course of making an article of jewelry from gold alloy stockmaterial in many instances the gold alloy stock is subjected tocoldworking, with the result that the finished article of jewelry willhave many places where the surface of the gold alloy is in a highlystressed condition and subject to this type of corrosion. A simpleexample would be where a sheet of gold alloy, either solid or plated, isformed to make a watch case. The material forming the bent-over rim ofthe case Will be in a stressed condition and subject tostress-corrosion.

This stressed condition is desirable in many instances because suchstresses may tend to give a desired stiffness to the finished article.Therefore, in these instances, it will not do to anneal the finishedarticle of jewelry to put it in an unstressed condition.

As an example of the effect of stress in hasten ing corrosion, thefollowing simple experiment may be cited:

Two pieces of metal of the same alloy were used for the experiment, thealloy being a standard stress-corrosion.

2 10 k. yellow gold having the composition (by weight):

Per cent Gold 41.66 Silver 7.67 Copper 41.97 Zinc 8.70

and each piece being approximately 2 inches long by A,, inch wide by.015 inch thick. The material from which these pieces were out hadpreviously been subjected to a reduction in thickness by passing itthrough a rolling mill. One of these pieces was then bent to bring itsends together, and these ends were fastened to maintain the piece inthis bent condition. The purpose of the bending is to create a place ofconcentrated tensile stress in the material. Then both of these pieces(one unbent, and the other bent and thus put under tensile stress) wereput in a 1% solution of ferric chloride, which is well known to be acorrosive reagent for gold alloys. The bent piece broke in two at theplace of bend in 30 seconds, whereas the unbent piece was substantiallyunaffected after several hours in the test solution.

The above example is also cited to illustrate a standard procedure fortesting for resistance to Itis, of course, an accelerated test, and thetime required for a specimen to break may be taken as a measure of theresistance to stress-corrosion.

This problem of stress-corrosion is particularly acute for the low-karatgold alloys, that is, the 8 to 12 karat alloys from which a largepercentage of costume jewelry is made today, and especially where thegold alloy is used only as a, thin plating over the base metal whichgoes to make up the bulk of the article of jewelry.

It is the general purpose of this invention, therefore, to provide agold alloy, and in particular one suitable for use in the jewelryindustry, having a high degree of resistance to stress-corrosion.

The stress-corrosion resistant gold alloy of this invention consistsbasically of gold, copper, and indium, the latter being present in thegold alloy in the percentages of 0.1% to 5.0% by weight. Assupplementary ingredients, it may also contain one or more of the metalssilver, zinc, and cadmium.

The quantity of gold present is determined by the desired karat of thegold. This invention is concerned chiefly with gold alloys of 8 to 12karat, consequently the proportion by Weight of the gold in the alloymay vary from approximately 33% to approximately 50%.

The copper content may vary from about 10.7% to about 67% by weight ofthe alloy, depending upon desired color, hardness, and other qualitiesof the finished alloy.

As stated above, the indium content of this invention is preferablywithin the range 0.1% to 5.0%;with 1.0% being a preferred quantity byweight. The'indium seems to act as an inhibitor of stress-corrosion andtends to whiten the alloy. If a quantity of indium substantially higherthan 5% is used, the resulting alloy tends to lack ductility and becomesdifiicult to cold work.

As to the supplementary'metals, the silver and V zinc (or cadmium) helpto get the desired color in the alloy. The zinc (or cadmium) stiffensthe alloy, acts as a deoxidizer, and helps in casting the alloy. Thesilver afiects the ductility of the alloy. Each of the silver, zinc,"and cadmium may be in the range of about 210% by weight.

While the stress corrosion resisting property of gold alloys issubstantially increased in all cases by the presence of indium in the.alloy, this increase isnot uniform, as is indicated in Table. I, whereinis shown the composition of the alloys tested (all being k.) and therelative stress corrosion, the latter being indicated by the timerequired for breaking of the test strip in an In Table II, for purposesof identification, there is given a series of 8, 10 and 12 karat goldalloys, by their compositions, one half of these alloys containing 1%indium, the other half not. Then in Table III there is shown the effectof the addition of the 1% indium on the stress corrosion properties ofthese alloys. It will be noted that in each case, the comparison is madebetween alloys of substantially the same composition, except for theaddition of the indium. For example alloy A is an 8 karat red goldalloy, and A-1 is substantially the same 8 karat red gold alloy with 1%indium added. Similarly, alloy B is an 8 karat yellow gold alloy, andalloy B1 is substantially the same 8 karat yellow gold alloy with 1%indium.

i has other advantages in gold alloys- Table III Cracking Time, AHOY 1%FeCl:

5 min. 15 sec.

12 min. 12 sec. 18 min. 23 sec. 50 min. 43 sec. 1 min. sec. 1 min. 52sec. 1 min. 48 sec. 24 hours 0. K.

1 min. 15 sec. 24 hours 0. K. l min. 10 sec. 5 min. 27 sec.

' In each of these alloys, it will be observed that the presence of theindium deters or inhibits stress-corrosion, increasing the time required(in the accelerated test used) for the corrosion cracks to appear.

In addition to the above described corrosionresisting effect "of theindium, the use of indium Among these may be noted the fact that theindium gold alloys of this invention are readily cold worked,

Table II Composition in Per Cent by Weight a Alloy Au Cu Ag Zn In TableIV HARDNESS-ROCKWELL 15T Annealed at 50% Reduction Alloy .030 inch at.015 inch thick thick The fact that these alloys are harder means thatthe alloy will wear better and that a piece of jewelry made from it willretain its surface finish over a-longer period of time. The factor ofless Work hardening means that it will be possible to make moreeconomically a finished piece of jewelry with the hardness of all of itsparts more uniform.

In the manufacture of the alloys of this invention, standard meltingprocedures may be used, care being taken to prevent loss of indium dueto its relatively low boiling point. It may be found necessary, in somecases, to add a little more indium than called for in the formula, inorder to take care of such loss. Such practice is Well known to thoseskilled in the art and need not be detailed here.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

As many changes could be made in the above alloys without departing fromthe scope of this invention, it is intended that all matter contained inthe above description shall be interpreted as illustrative and not in alimiting sense.

I clam:

1. A stress-corrosion resistant gold alloy consisting essentially ofgold, about 33-50%; indium, about 0.1 to 5%; at least one coloring metalselected from the group consisting of silver, zinc, and cadmium each inan amount in the range of 210%; and balance, copper but not less thanabout 10.7% all by weight 2. A stress-corrosion resistant gold alloyconsisting essentially of gold, about 33 to 50%; indium, about 0.1 to 5%silver, about 2 to zinc, about 210%; and balance, copper but not lessthan about 10.7%; all by weight.

3. A stress-corrosion resistant gold alloy consisting essentially ofgold, about 33 to 50%; indium, about 0.1 to 5%; silver, about 2-10%;cadmium, about 2-10%; and balance, copper but not less than about 10.7%;all by weight.

4. A stress-corrosion resistant gold alloy consisting essentially ofgold, about 33% to 50%; indium, about 0.1 to 5%; silver, about 2 to 10%:and balance, copper but not less than about 10.7% all by weight.

5. A stress-corrosion resistant gold alloy consisting essentially ofgold, about 33 to 50%; indium, about 0.1 to 5%; zinc, about 240%; andbalance, copper but not less than about 10.7 all by weight.

6. A stress-corrosion resistant gold alloy consisting essentially ofgold, about 33 to 50%; indium, about 0.1 to 5%; cadmium, about 240%; andbalance, copper but not less than about 10.7 all by weight.

JOSEPH M. WILLIAMS.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 1,090,939 Newton Mar. 24, 19141,965,012 Taylor July 3, 1934 1,987,451 Taylor Jan. 8, 1935 2,371,240Hensel et al. Mar. 213, 1945 2,400,003 Hensel et al. May 7, 19462,438,967 Ellsworth Apr. 6, 1948 FOREIGN PATENTS Number Country Date209,975 Great Britain Jan. 24, 1924 218,138 Switzerland Mar. 16, 1942OTHER REFERENCES Ludwick, Treatise in Metal Finishing, January 1942, pp.13-17, inclusive.

Product Engineering, October 1943, pp. 630- 632, inclusive.

1. A STRESS-CORROSION RESISTANT GOLD ALLOY CONSISTING ESSENTIALLY OFGOLD, ABOUT 33-50%; INDIUM, ABOUT 0.1 TO 5%; AT LEAST ONE COLORING METALSELECTED FROM THE GROUP CONSISTING OF SILVER, ZINC, AND CADMIUM EACH INAN AMOUNT IN THE RANGE OF 2-10%; AND BALANCE, COPPER BUT NOT LESS THANABOUT 10.7%; ALL BY WEIGHT